Video: Impact Caused Tesla Battery Fire

A fire in a Tesla Model S electric sedan has once again placed a spotlight on the issue of lithium-ion battery safety.

The incident, captured on a now-viral video (watch it below), occurred after the vehicle rolled down an off-ramp in a suburban area between Seattle and Tacoma, Wash. Soon after it stopped and the driver exited, the car's front end was engulfed in flames.

In a statement emailed to Design News, Tesla wrote:

The fire was caused by the direct impact of a large metallic object to one of the 16 modules within the Model S battery pack. Because each module of the battery pack is, by design, isolated by fire barriers to limit any potential damage, the fire in the battery pack was contained to a small section in the front of the vehicle.

A CT scan image of a battery cell shows breakdown of layers directly below an indentation. A recent report from Underwriters’ Laboratories Inc. suggests that such dents in the casing are a possible failure mechanism for lithium-ion batteries. “The resulting high stress/strain will lead to a mechanical failure of the separator (with failure of the casing), allowing for direct contact between electrodes at a distance only a few layers below the casing surface,” the report says. (Source: Underwriters Laboratories Inc.)

A fire incident report from the Regional Fire Authority of Kent, Wash., stated that firefighters appeared to have extinguished the fire, only to have it restart underneath the Model S, in the area of the battery. Applying water through puncture holes, the report said, only "seemed to intensify the activity." Firefighters ultimately doused the flames after dismantling the front end of the vehicle, cutting an access hole with a circular saw, and applying a "dry chemical agent," the report said.

"The vehicle's driver stated that he had struck some kind of object on the freeway," the report added. "He stated that he then began to have problems with the vehicle and pulled off the freeway."

Battery experts told Design News that it's hard to say exactly what happened until more details are available. "It could be an indentation or it could be a puncture incident where you have physical breaching of the battery pack," Ken Boyce, Underwriter Laboratories'
principal engineering manager for energy, told Design News. "Depending on what actually happened, there could be a number of failure mechanisms."

The fact that the battery pack was struck by a metal object raises the possibility of internal shorts, experts told us. "I find it disturbing that they had the fire," Ralph Brodd, a well-known lithium battery expert and founder of the consultancy, Broddarp of Nevada, told us. "It tells you that their case may not have been sturdy enough."

Mechanical deformation of a battery's casing can be particularly problematic for high-energy lithium-ion batteries, experts said. "In a lithium-ion battery, you've got electrodes that are tens of microns from one another," Elton Cairns, a professor of chemical and biomolecular engineering at the University of California-Berkeley said during a 2011 discussion with Design News. "If you deform the cell case and it causes the electrodes to touch one another, there's an internal short circuit. That can cause the cell to rapidly discharge and, in so doing, heat up."

Such occurrences are rare, however. A Tesla spokeswoman told Design News that the Model S has collectively been driven 83 million miles at this point, with dozens of known accidents, and no such battery problems, until now.

Lithium-ion batteries have recently grabbed headlines after notable overheating incidents caused by short-circuiting. In the Boeing 787, the cause of the short circuiting was never pinned down. In the highly publicized Chevy Volt incident of 2011, the fire was determined to have occurred when coolant came in contact with a printed circuit board during government tests. GM subsequently beefed up the Volt with structural enhancements, emphasizing that the changes had nothing to do with the battery itself, which engineers described as safe.

"This is the challenge with these battery packs," said Boyce of UL. "You have a lot of energy condensed into a very small footprint. That's why you use it, but it's also what makes it so challenging."

Warning: This video contains profanity. If you don't wish to hear it, please do not click on the video.

Chuck, Didn't Tesla get a top safety rating just recently for the S? This is a problem with EVs (and hybrids) that use Lithium Ion batteries. I am not sure that the testing agancies really know how to characterize the failure modes of these batteries. As I have mentioned before, there was an incident in China where an all electric cab of local manufacture caught fire and burned up the driver and passengers completely after a collision with a car that drove away. This is very worrisome.

Since the Tesla Model S batteries can be swapped out in a few seconds at their roadside stations, there must be some sort of quick release that would make it possible in an emergency to drop the battery pack and roll the car away from it, thereby saving the vehicle in case of battery fire.

Perhaps there should be a small, separate battery just for the purpose of driving the vehicle a few feet to get off of and away from the dropped main battery.

You're right on the money, naperlou. Yes, Tesla has "fives" (best rating) across the board in NHTSA's safety ratings. And, yes, the methodology for the ratings is well established. I agree that the ratings agencies don't yet have a handle on how to characterize the relatively new phenomenon of lithium-ion failures.

Ken, my understanding of the battery swap out machine is that it simultaneously unscrews a large number of bolts, drops the battery down, then raises another battery up into place. Reportedly, it is the same piece of equipment they use in the factory. It is not a mobile piece of equipment. In videos of it working, the car is driven up over the device. This is not a quick relesae mechanism. The device reportedly will cost Tesla $500K to intsall.

If the battery is susceptible to being breached the way this one was, any auxiliary battery would be susceptible as well. If it was anywhere near the part tha caught fire, it would also catch fire. Also, the battery weighs over 900 lbs., so I am not sure your idea would work.

I think the idea of having the battery basically cover the bottom of the car is a very bad one. This could prove their undoing. Now they will probably have to put some sort of shielding there. That will increase the weight even more.

"Such occurrences are rare, however. A Tesla spokeswoman told Design News that the Model S has collectively been driven 83 million miles at this point, with dozens of known accidents, and no such battery problems, until now."

Seems to me that this is a misleading statement and is a poor defense for Tesla battery safety. 83 million miles refers to driving distance but does not take into account an impact with an object - and "dozens of known accidents" does not give any quantifiable data regarding this specific issue.

apparently the battery has an armor plate beneath it, 1/4" thick. However,

hit something hard enough, fast enough and it will rip through almost anything.

Lets not forget some minor ice sank the Titanic.

Now that said, Lou's idea of dropping the battery pack isn't neccessarily a bad idea.

if you have a fire, it would seem easiest to have some explosive bolts on the body side, that would cut the structural attachments and let the battery drop off. You would need a small internal battery to drive away, but, it could be done as a future upgrade.

Wow that is scary stuff! It's unfortunate this keeps happening, because it certainly isn't going to do anything to promote the use of hybrid vehicles and EVs. It's especially troubling because of Tesla's high rating, as Lou points out.

So the Pinto, Chevy saddle tanks, and the recent Jeep recalls should all be put aside if we let the Tesla get a pass?

On the otherhand, debris is a part of the road. If consumers expect the cars to be 100% safe, then the only solution is to get rid of the car. At least in this instance, the driver was able to pull over and get out. In fact, I think this was explicitily discussed when many here at DN were critical of the Boeing batteries. Lithium ion chemistry in an airplane, not so good as the option is a plane crash (or crash landing). But in an automobile one could pull over and get out of the car.

Earlier this year paralyzed IndyCar drive Sam Schmidt did the seemingly impossible -- opening the qualifying rounds at Indy by driving a modified Corvette C7 Stingray around the Indianapolis Motor Speedway.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.